Zoom lens and image pickup apparatus having the same

Abstract

A zoom lens includes: a first lens unit of positive refractive power; a second lens unit of negative refractive power; a third lens unit of positive refractive power; and a fourth lens unit of positive refractive power, being disposed in that order from an object side to an image side, in which the second and fourth lens units are moved in a direction parallel with an optical axis of the zoom lens during zooming, the first lens unit consists of one negative lens and three or fewer positive lenses, being disposed in that order from the object side to the image side, and the following condition is satisfied: 25.1< Z×BD 1/ BD 2<4.1× Z, where BD1 and BD2 are lengths of the first and second lens units along the optical axis, and Z is a zoom ratio.

1. A zoom lens comprising:
 a first lens unit of positive refractive power; 
 a second lens unit of negative refractive power; 
 a third lens unit of positive refractive power; and 
 a fourth lens unit of positive refractive power, being disposed in that order from an object side to an image side, wherein 
 the second and fourth lens units are moved in a direction parallel with an optical axis of the zoom lens during zooming, 
 the first lens unit consists of one negative lens and three or fewer positive lenses, being disposed in that order from the object side to the image side, and 
 the following condition is satisfied:
   25.1 <Z×BD 1/ BD 2<4.1 ×Z,    
 
  where BD1 and BD2 are lengths of the first and second lens units along the optical axis, and Z is a zoom ratio. 
 
   
   
     2. The zoom lens according to  claim 1 , wherein
 the third lens unit comprises a third-a lens sub-unit of negative refractive power and a third-b lens sub-unit of positive refractive power, being disposed in that order from the object side to the image side, and 
 the third-b lens sub-unit is moved in a direction orthogonal to the optical axis so as to shift an image. 
 
   
   
     3. The zoom lens according to  claim 2 , wherein the third-b lens sub-unit comprises a positive lens including an aspherical surface, a negative lens, and a positive lens, being disposed in that order from the object side to the image side. 
   
   
     4. The zoom lens according to  claim 1 , wherein
 the first lens unit consists of a negative lens G 11 , a positive lens G 12 , a positive lens G 13 , and a positive lens G 14 , being disposed in that order from the object side to the image side, 
 at least one of the following conditions are satisfied:
   75<ν dG 12, 
   65<ν dG 13, 
   1.601< NdG 14<1.811, 
 
  where νdG 12  and νdG 13  are Abbe numbers of materials of the positive lenses G 12  and G 13 , and NdG 14  is a refractive index of a material of the positive lens G 14 . 
 
   
   
     5. The zoom lens according to  claim 1 , wherein
 the second lens unit has a negative lens, and at least one positive lens G 2 p on the image side of the negative lens, and 
 the following condition is satisfied:
   ν dG 2 p< 23.5, 
 
  where νdG 2 p is an Abbe number of a material of the positive lens G 2 p. 
 
   
   
     6. The zoom lens according to  claim 5 , wherein the positive lens G 2 p is affixed to a negative lens. 
   
   
     7. The zoom lens according to  claim 1 , wherein the first lens unit consists of the negative lens and three positive lenses. 
   
   
     8. The zoom lens according to  claim 1 , wherein the zoom lens consists of four lens units. 
   
   
     9. The zoom lens according to  claim 1 , wherein the zoom lens is adapted to form an image of an object on a solid-state image pickup element. 
   
   
     10. An image pickup apparatus comprising:
 a solid-state image pickup element; and 
 a zoom lens arranged to form an image of an object on the solid-state image pickup element, wherein 
 the zoom lens includes:
 a first lens unit of positive refractive power; 
 a second lens unit of negative refractive power; 
 a third lens unit of positive refractive power; and 
 a fourth lens unit of positive refractive power, being disposed in that order from an object side to an image side, 
 
 the second and fourth lens units are moved in a direction parallel with an optical axis of the zoom lens during zooming, 
 the first lens unit consists of one negative lens and three or fewer positive lenses, being disposed in that order from the object side to the image side, and 
 the following condition is satisfied:
   25.1 <Z×BD 1/ BD 2<4.1 ×Z,    
 
  where BD1 and BD2 are lengths of the first and second lens units along the optical axis, and Z is a zoom ratio.